JP2005268898A - Bandpass filter circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To fully prevent mutual interference even if many radio machines are operated simultaneously without making a circuit configuration complex. <P>SOLUTION: Transmission waves from the radio machine 10 are outputted from a second port (b) of a first circulator 11, are totally reflected by a first BEF 22, are inputted to the second port (b), are outputted from a third port (c), and are inputted to a second circulator 14. The transmission waves in which transmission noise components are removed are transmitted from an antenna 17 through the second circulator 14. The reception waves received by the antenna 17 are outputted from the second port (b) of the second circulator 14, are totally reflected by a second BEF 25, are inputted to the second port (b), are outputted from a first port (a), and are inputted to the first circulator 11. Reception waves in which interference wave components are removed are received by the radio machine 10 through the first circulator 11. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a bandpass filter circuit that reduces mutual interference between double-trusted radios that occurs in a double-trusted radio whose transmission frequency and reception frequency are different.

  There is full-duplex communication in which data can be transmitted and received from both sides simultaneously in the bidirectional communication system. This full-duplex communication can be realized by preparing two frequencies by preparing different frequencies for the uplink and downlink. The double-trust radio device used when this full-duplex communication is performed using a radio line is a double-trust radio device to which different frequencies are assigned for the transmission frequency and the reception frequency.

When such duplex radios are operated at the same time, transmission signals are always transmitted, so that they are liable to cause interference with each other, and there is a possibility that communication may be hindered by mutual interference. Therefore, conventionally, to prevent mutual interference by changing the frequency used for each double-trusted radio so as not to cause mutual interference, arranging the double-trusted radio at intervals, or reducing transmission power. I was doing.
However, in recent wireless systems based on digitization and the like, there is a wireless system that performs duplex communication by assigning different frequencies between a transmission frequency and a reception frequency and switching between transmission and reception in a time division manner. In this way, when duplex duplex radios that switch between transmission and reception in time division are operated simultaneously, the duplex radio does not have an antenna duplexer and has a transmission filter and a reception filter. As a result, there is a risk that a communication failure may occur due to a reception failure caused by a transmission signal of an adjacent wireless device.

Conventionally, in order to solve this problem, it has been proposed to insert the band-pass filter circuit 100 shown in FIG. 8 between the radio 110 and the antenna 116.
In the band-pass filter circuit 100 shown in FIG. 8, the first port a is connected to the radio 110, the second port b is connected to the first band-pass filter (BPF) 112, and the third port c is connected. The first port a is connected to the first circulator 111 connected to the second bandpass filter (BPF) 115 and the first bandpass filter (BPF) 112, and the second port b is connected to the antenna 116. And a second circulator 113 having a third port c connected to the isolator 114. The first BPF 112 has a characteristic of allowing only the transmission frequency band transmitted by the radio 110 to pass, and the second BPF 115 has a characteristic of allowing only the reception frequency band received by the radio 110 to pass.

In the band-pass filter circuit 100, the transmission path of the transmission wave and the transmission path of the reception wave are arranged in parallel. Explaining the transmission path of a transmission wave, a transmission wave of a predetermined transmission frequency transmitted from the radio 110 is input to the first port a of the first circulator 111 and output from the second port b thereof. Input to the first BPF 112. In the first BPF 112, only the band of the transmission wave transmitted from the radio device 110 passes through and is output, and this output is input to the first port a of the second circulator and output from the second port b. And transmitted from the antenna 116.
Next, the transmission path of the received wave will be described. The received wave received by the antenna 116 is input to the second port b of the second circulator 113 and output from the third port c via the isolator 114. And input to the second BPF 115. In the second BPF 115, only the band of the received wave to be received by the wireless device 110 passes through and is output. This output is input to the third port c of the first circulator 111, output from the first output port a, and received by the radio device 110.

  The operation of the isolator 114 is as follows. In the BPF 112, only the transmission frequency band transmitted by the wireless device 110 is allowed to pass, and other frequency components are reflected. The frequency component reflected by the BPF 112 is input to the second port b of the circulator 111 and output from the third port c of the circulator 111 so as to be input to the BPF 115. In the BPF 115, a signal in a reception frequency band received by the wireless device 110 passes through the BPF 115, and the signal that passes through the BPF 115 is terminated by the isolator 114. Here, when the isolator 114 is not provided, the signal that has passed through the BPF 115 is input to the third port c of the circulator 113, output from the first port a, and further reflected by the BPF 112. Since the reflected signal is input to the first port a of the second circulator 113 again, output from the second port b, and radiated from the antenna 116, the band of the reception frequency that becomes the transmission noise component is obtained. The signal will be transmitted. In this way, the isolator 114 is configured not to transmit a signal in the band of the reception frequency that becomes a transmission noise component.

  As described above, the first band-pass filter 112 that passes only the band of the transmission wave by the band-pass filter circuit 100 removes the transmission noise component, and the second band that passes only the band of the reception wave. Since the interference wave component is removed by the bandpass filter 115 and received, the mutual interference can be sufficiently prevented even when many radio devices are operated simultaneously. However, the band-pass filter circuit 100 shown in FIG. 8 has a problem in that an isolator is required, so that the number of parts increases, and the size cannot be reduced and the cost is increased.

  Accordingly, an object of the present invention is to provide a band-pass filter circuit that can reduce the number of parts, can be miniaturized, and can reduce the cost.

  In order to achieve the above object, a band-pass filter circuit according to the present invention includes a first filter that passes only a first signal of a defined first frequency band input to a first input / output unit; And a second filter that passes only the second signal in the prescribed second frequency band output from the second input / output means, and the signal reflected by the first filter is input to the second input / output The main feature is that the signal is output from the means and the signal reflected by the second filter is input to the first input / output means.

  According to the present invention, the first filter that passes only the first signal in the defined first frequency band that is input to the first input / output unit, and the definition that is output from the second input / output unit. And a second filter that allows only the second signal in the second frequency band to pass through, the signal reflected by the first filter being output from the second input / output means, and the second filter The signal reflected by the filter is input to the first input / output means. As a result, it is possible to provide a band-pass filter circuit that can eliminate the need for an isolator, reduce the size, and reduce the cost.

  For the purpose of providing a band-pass filter circuit that can reduce the number of parts, can be reduced in size, and can be reduced in cost, a defined first input to the first input / output means is provided. A first filter that passes only the first signal in the frequency band; and a second filter that passes only the second signal in the specified second frequency band output from the second input / output means. The signal reflected by the first filter is output from the second input / output means, and the signal reflected by the second filter is input to the first input / output means. It was realized.

The configuration of an embodiment of the band-pass filter circuit of the present invention is shown in FIG.
The band-pass filter circuit 1 according to the embodiment of the present invention shown in FIG. 1 is installed by being inserted between a double trust radio device 10 and an antenna 17. The band-pass filter circuit 1 includes a first circulator 11 and a second circulator 14 connected in cascade. The first circulator 11 has a transmission frequency band assigned to the radio 10 at least as a stop band. The second circulator 14 is connected with a filter B15 whose reception frequency band assigned to the radio device 10 is at least a stop band. The band-pass filter circuit 1 according to the present invention having such a configuration is an irreversible circuit having different transmission characteristics depending on a high-frequency transmission direction as a transmission wave and a reception wave.

  The operation of the bandpass filter circuit 1 when a transmission wave is transmitted will be described. The transmission wave transmitted from the wireless device 10 is input to the first port a of the first circulator 11 and the second port thereof. b is input to the filter A12. Since the stop band of the filter A12 is at least the band of the transmission frequency assigned to the radio device 10, the transmission frequency component of the transmission wave transmitted from the radio device 10 is totally reflected by the filter A12 and the first circulator. 11 to the second port b. The transmission noise component outside the transmission frequency band included in the transmission wave passes through the filter A12 and is absorbed by the termination resistor 13. In this way, the transmission wave from which the unnecessary wave component input to the second port b of the first circulator 11 is removed is output from the third port c of the first circulator to be output to the second circulator 14. To the first port a. The transmission wave input to the first port a of the second circulator 14 is output from the third port c of the second circulator 14 and supplied to the antenna 17 to remove the transmission noise component. Is transmitted from the antenna 17.

  Next, the operation of the bandpass filter circuit 1 when a received wave having a different frequency band from that of the transmitted wave is transmitted will be described. The received wave received by the antenna 17 is the third circulator 14 of the third circulator 14. The signal is input to the port c, output from the second port b, and input to the filter B15. Since the stop band of the filter B15 is at least the band of the reception frequency assigned to the radio device 10, the frequency component to be received of the reception wave received by the antenna 17 is totally reflected by the filter B15 and the second frequency is received. Input to the second port b of the circulator 14. Then, the interference wave component outside the reception frequency band included in the reception wave passes through the filter B15 and is absorbed by the termination resistor 16. In this way, the received wave from which the interference wave component input to the second port b of the second circulator 14 is removed is output from the first port a of the second circulator 14 to be output to the first circulator. 11 to the third port c. The received wave input to the third port c of the first circulator 11 is output from the first port a of the first circulator 11, supplied to the radio device 10, and received by the radio device 10. become.

As described above, the transmission wave transmitted from the radio device 10 passes through the second circulator 14 and thus is not affected by the filter B15, and the reception wave received by the antenna 17 is not affected by the first circulator 11. So that it is not affected by the filter A12. As described above, the band-pass filter circuit 1 of the present invention is irreversible with different transmission characteristics depending on the transmission direction of the transmission wave / reception wave, and becomes a band-pass filter circuit 1 suitable for the dual-trust radio device 10. Moreover, since an isolator can be made unnecessary in principle, the number of parts can be reduced, the size can be reduced, and the cost can be reduced.
Note that what is connected to the first port a of the first circulator 11 is not limited to the radio 10 and outputs an output signal in a predetermined frequency band, and an input signal in a different frequency band is input. The input / output means connected to the third port c of the second circulator 14 is not limited to the antenna 17 and may be any input / output means having an input / output function. Conversely, input / output means having an input / output function is connected to the first port a of the first circulator 11, and an output signal of a predetermined frequency band is connected to the third port c of the second circulator 14. And an input / output means to which an input signal in a different frequency band is input may be connected.

  Next, FIG. 2 shows frequency characteristics of the first embodiment of the filter A12 and the filter B15. As shown in this figure, the filter A12 and the filter B15 are configured by band elimination filters. A notch filter, which is a band elimination filter, is a filter that easily obtains steep characteristics with a simple configuration. As shown in FIG. 2, the filter A <b> 12 configured by the band elimination filter has a stop band set to a transmission frequency band Bt in the radio device 10. As a result, only the component of the transmission frequency band Bt is reflected by the filter A12, and the component that becomes transmission noise passes and is absorbed by the termination resistor 13. The component of the transmission frequency band Bt reflected by the filter A12 is transmitted from the antenna 17. However, since the cutoff characteristic of the filter A12 configured by the band elimination filter is steep, it is transmitted from the antenna 17. The transmission noise component is sufficiently removed from the transmitted wave, so that mutual interference can be sufficiently prevented.

  Further, as shown in FIG. 2, the filter B <b> 15 configured by the band elimination filter has a reception band of the reception frequency band Br in the radio device 10. As a result, only the component of the reception frequency band Br is reflected by the filter B15, and the component that becomes an interference wave passes and is absorbed by the terminating resistor 16. The component of the reception frequency band Br reflected by the filter B15 is received by the radio device 10, but the cutoff characteristic of the filter B15 configured by the band elimination filter is steep, so that the antenna 17 The interference wave component is sufficiently removed from the received reception wave, and it is possible to sufficiently prevent a reception failure.

  Next, FIG. 3 shows the frequency characteristics of the second embodiment of the filter A12 and the filter B15. As shown in this figure, the filter A12 and the filter B15 are composed of bandpass filters. As shown in FIG. 3, the filter A <b> 12 configured by a bandpass filter has a passband that is a reception frequency band Br in the radio device 10 and a transmission frequency band Bt that belongs to a stopband. As a result, the component of the reception frequency band Br that becomes transmission noise in the filter A12 passes and is absorbed by the termination resistor 13, and the component of the transmission frequency band Bt is reflected. The component of the transmission frequency band Bt reflected by the filter A12 is transmitted from the antenna 17. However, since the cutoff characteristic of the filter A12 configured by the bandpass filter is sufficiently steep, it is transmitted from the antenna 17. The transmission noise component is sufficiently removed from the transmitted wave, so that mutual interference can be sufficiently prevented.

  Further, as shown in FIG. 3, the filter B <b> 15 configured by a band pass filter has a pass band that is a transmission frequency band Bt in the radio device 10 and a reception frequency band Br that belongs to a stop band. As a result, a component that becomes an interference wave in the filter B15 passes and is absorbed by the termination resistor 16, and a component in the reception frequency band Br is reflected. Although the component of the reception frequency band Br reflected by the filter B15 is received by the radio device 10, the cutoff characteristic of the filter B15 formed by the bandpass filter is sufficiently steep, so that the antenna 17 The interference wave component is sufficiently removed from the received reception wave, and it is possible to sufficiently prevent a reception failure.

  Next, FIG. 4 shows frequency characteristics of the third embodiment of the filter A12 and the filter B15. As shown in this figure, the filter A12 is composed of a bandpass filter, and the filter B15 is composed of a band elimination filter. As shown in FIG. 4, the filter A <b> 12 configured by a bandpass filter has a passband that is a reception frequency band Br in the radio device 10 and a transmission frequency band Bt that belongs to a stopband. As a result, the component of the reception frequency band Br that becomes transmission noise in the filter A12 passes and is absorbed by the termination resistor 13, and the component of the transmission frequency band Bt is reflected. The component of the transmission frequency band Bt reflected by the filter A12 is transmitted from the antenna 17. However, since the cutoff characteristic of the filter A12 configured by the bandpass filter is sufficiently steep, it is transmitted from the antenna 17. The transmission noise component is sufficiently removed from the transmitted wave, so that mutual interference can be sufficiently prevented.

  Further, as shown in FIG. 4, the filter B <b> 15 configured by the band elimination filter has a stop band set to the reception frequency band Br in the radio device 10. As a result, only the component of the reception frequency band Br is reflected by the filter B15, and the component that becomes an interference wave passes and is absorbed by the terminating resistor 16. The component of the reception frequency band Br reflected by the filter B15 is received by the wireless device 10, but the cutoff characteristic of the filter B15 configured by the band elimination filter is steep, so that the antenna 17 The interference wave component is sufficiently removed from the received reception wave, and it is possible to sufficiently prevent a reception failure.

  Next, FIG. 5 shows frequency characteristics of the fourth embodiment of the filter A12 and the filter B15. As shown in this figure, the filter A12 is composed of a band elimination filter, and the filter B15 is composed of a bandpass filter. As shown in FIG. 5, the filter A <b> 12 configured by the band elimination filter has a stop band set to the transmission frequency band Bt in the radio device 10. As a result, the component of only the transmission frequency band Bt is reflected by the filter A12, and the component that becomes transmission noise passes and is absorbed by the termination resistor 13. The component of the transmission frequency band Bt reflected by the filter A12 is transmitted from the antenna 17. However, since the cutoff characteristic of the filter A12 configured by the band elimination filter is steep, it is transmitted from the antenna 17. The transmission noise component is sufficiently removed from the transmitted wave, so that mutual interference can be sufficiently prevented.

  Further, as shown in FIG. 5, the filter B15 configured by a bandpass filter has a passband that is a transmission frequency band Bt in the wireless device 10 and a reception frequency band Br that belongs to a stopband. As a result, a component that becomes an interference wave in the filter B15 passes and is absorbed by the termination resistor 16, and a component in the reception frequency band Br is reflected. Although the component of the reception frequency band Br reflected by the filter B15 is received by the radio device 10, the cutoff characteristic of the filter B15 formed by the bandpass filter is sufficiently steep, so that the antenna 17 The interference wave component is sufficiently removed from the received reception wave, and it is possible to sufficiently prevent a reception failure.

FIG. 6 shows a specific configuration in which the filter A12 and the filter B15 in the bandpass filter circuit according to the present invention described above have the frequency characteristics of the first embodiment. In the bandpass filter circuit 2 shown in FIG. 6, the filter A12 is a first band elimination filter (BEF) 22 and the filter B15 is a second band elimination filter (BEF) 25.
In the bandpass filter circuit 2 shown in FIG. 6, the first BEF 22 has a stop band set to the transmission frequency band Bt in the radio device 10. As a result, only the component of the transmission frequency band Bt is reflected by the first BEF 22, and the component that becomes the transmission noise passes and is absorbed by the termination resistor 13. Although the component of the transmission frequency band Bt reflected by the first BEF 22 is transmitted from the antenna 17, the cutoff characteristic of the filter A12 configured by the band elimination filter is steep, so that the antenna 17 The transmission noise component is sufficiently removed from the transmission wave transmitted from, so that mutual interference can be sufficiently prevented.

  In addition, the second BEF 25 has a stop band that is the reception frequency band Br in the radio device 10. As a result, only the component of the reception frequency band Br is reflected by the filter B15, and the component that becomes an interference wave passes and is absorbed by the terminating resistor 16. The component of the reception frequency band Br reflected by the filter B15 is received by the radio device 10, but the cutoff characteristic of the second BEF 25 configured by the band elimination filter is steep, so that the antenna The interference wave component is sufficiently removed from the received wave received at 17, so that it is possible to sufficiently prevent a reception failure.

FIG. 7 shows a graph of frequency characteristics indicating the transmission characteristics of the bandpass filter circuit 2 shown in FIG. In this case, for example, the transmission frequency band Bt of the radio device 10 is 160 ± 0.6 MHz, and the reception frequency band Br is 156 ± 0.6 MHz.
As described above, the transmission characteristics of the bandpass filter circuit 1 are irreversible when the transmission wave is directed to the antenna 17 and when the reception wave is directed to the radio device 10. In FIG. 7, the transmission characteristic of the transmission wave toward the antenna 17 is indicated by To ANT, and the transmission characteristic of the reception wave toward the radio device 10 is indicated by From ANT. Referring to FIG. 7, in the transmission characteristics of the transmission wave, it can be seen that the transmission loss is about 1.5 dB in the transmission frequency band Bt, and an attenuation of about 24 dB or more is obtained in the reception frequency band Br. Further, in the transmission characteristics of the received wave, it can be seen that the passage loss is about 1 dB in the reception frequency band Br, and an attenuation of about 20 dB or more is obtained in the transmission frequency band Bt.

  In the above description, the band-pass filter circuit provided between the radio and the antenna or the band-pass filter circuit provided between the first input / output means and the second input / output means is described. Is not limited to this, and can be generally used as a circuit that requires irreversible band-pass characteristics.

It is a figure which shows the structure of the Example of the band pass filter circuit of this invention. It is a figure which shows the frequency characteristic of the 1st Example of the filter A and the filter B in the band pass filter circuit of this invention. It is a figure which shows the frequency characteristic of 2nd Example of the filter A and the filter B in the band pass filter circuit of this invention. It is a figure which shows the frequency characteristic of the 3rd Example of the filter A and the filter B in the band pass filter circuit of this invention. It is a figure which shows the frequency characteristic of the 4th Example of the filter A and the filter B in the band pass filter circuit of this invention. It is a figure which shows the specific structure of the band pass filter circuit of this invention. It is a graph which shows the transmission characteristic in the specific structure of the band pass filter circuit of this invention. It is a figure which shows the structure of the conventional band pass filter circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Band pass filter circuit, 2 Band pass filter circuit, 10 Radio | wireless machine, 11 1st circulator, 12 Filter A, 13 Termination resistance, 14 2nd circulator, 15 Filter B, 16 Termination resistance, 17 Antenna, 22 1st Band elimination filter, 25 second band elimination filter, 100 band pass filter circuit, 110 radio, 111 first circulator, 112 first band pass filter, 113 second circulator, 114 isolator, 115 second 2 bandpass filters, 116 antennas, Br reception frequency band, Bt transmission frequency band

Claims (6)

A first signal only in the specified first frequency band is input to the first input / output means, and a second signal only in the specified second frequency band is output from the second input / output means. A band-pass filter circuit provided between the first input / output means and the second input / output means,
A first port connected to the first input / output means, a second port to which a first filter that passes only the component of the first frequency band is connected, and a third port A first circulator having,
A first port to which a third port of the first circulator is connected; a second port to which a second filter that passes a component of the second frequency band is connected; and the second port A second circulator having a third port to which the input / output means is connected,
A signal input from the first input / output means to the first port of the first circulator is output from the second port and output to the first filter. Components other than those in the first frequency band are reflected and output from the third port of the first circulator, input to the first port of the second circulator, and output from the third port. And being supplied to the second input / output means, the second signal of only the second frequency band is output from the second input / output means,
A signal input from the second input / output means to the third port of the second circulator is output from the second port to the second filter, and the second filter outputs the signal. Components other than those in the second frequency band are reflected and output from the first port of the second circulator, input to the third port of the first circulator, and output from the first port. And the first input / output means supplies the first signal of only the first frequency band to the first input / output means. A first signal only in the prescribed first frequency band is input to the first input / output means, and a second signal only in the prescribed second frequency band is outputted from the second input / output means. And a band-pass filter circuit provided between the first input / output means and the second input / output means,
A first port connected to the first input / output means; a second port connected to a first filter for blocking a component of the second frequency band; and a third port. A first circulator;
A first port to which a third port of the first circulator is connected; a second port to which a second filter for blocking a component of the first frequency band is connected; and the second port A second circulator having a third port to which the input / output means is connected,
A signal input from the first input / output means to the first port of the first circulator is output from the second port and output to the first filter. The component of the second frequency band is reflected and output from the third port of the first circulator, input to the first port of the second circulator, output from the third port, and By being supplied to the second input / output means, the second signal of only the second frequency band is output from the second input / output means,
A signal input from the second input / output means to the third port of the second circulator is output from the second port to the second filter, and the second filter outputs the signal. A component of the first frequency band is reflected and output from the first port of the second circulator, input to the third port of the first circulator, output from the first port, and A band-pass filter circuit characterized in that the first signal of only the first frequency band is input to the first input / output means by being supplied to the first input / output means. A first signal only in the prescribed first frequency band is input to the first input / output means, and a second signal only in the prescribed second frequency band is outputted from the second input / output means. And a band-pass filter circuit provided between the first input / output means and the second input / output means,
A first port connected to the first input / output means, a second port to which a first filter that passes only the component of the first frequency band is connected, and a third port A first circulator having,
A first port to which a third port of the first circulator is connected; a second port to which a second filter for blocking a component of the first frequency band is connected; and the second port A second circulator having a third port to which the input / output means is connected,
A signal input from the first input / output means to the first port of the first circulator is output from the second port and output to the first filter. Components other than those in the first frequency band are reflected and output from the third port of the first circulator, input to the first port of the second circulator, and output from the third port. And being supplied to the second input / output means, the second signal of only the second frequency band is output from the second input / output means,
A signal input from the second input / output means to the third port of the second circulator is output from the second port to the second filter, and the second filter outputs the signal. A component of the first frequency band is reflected and output from the first port of the second circulator, input to the third port of the first circulator, output from the first port, and A band-pass filter circuit characterized in that the first signal of only the first frequency band is input to the first input / output means by being supplied to the first input / output means. A first signal only in the prescribed first frequency band is input to the first input / output means, and a second signal only in the prescribed second frequency band is outputted from the second input / output means. And a band-pass filter circuit provided between the first input / output means and the second input / output means,
A first port connected to the first input / output means; a second port connected to a first filter for blocking a component of the second frequency band; and a third port. A first circulator;
A first port to which a third port of the first circulator is connected; a second port to which a second filter that passes a component of the second frequency band is connected; and the second port A second circulator having a third port to which the input / output means is connected,
A signal input from the first input / output means to the first port of the first circulator is output from the second port and output to the first filter. The component of the second frequency band is reflected and output from the third port of the first circulator, input to the first port of the second circulator, output from the third port, and By being supplied to the second input / output means, the second signal of only the second frequency band is output from the second input / output means,
A signal input from the second input / output means to the third port of the second circulator is output from the second port to the second filter, and the second filter outputs the signal. Components other than those in the second frequency band are reflected and output from the first port of the second circulator, input to the third port of the first circulator, and output from the first port. And the first input / output means supplies the first signal of only the first frequency band to the first input / output means. A band-pass filter circuit provided between the radio and the antenna,
A first port connected to the radio, a second port connected to a first band elimination filter having a transmission frequency band to be transmitted by the radio as a stop band, and a third port A first circulator having:
A first port to which a third port of the first circulator is connected is connected to a second band elimination filter having a reception frequency band to be received by the radio as a stop band. And a second circulator having a third port to which an antenna is connected,
A transmission wave input from the wireless device to the first port of the first circulator is output from the second port and output to the first band elimination filter, and the first band elimination The transmission frequency band component of the transmission wave is reflected by the filter and output from the third port of the first circulator, input to the first port of the second circulator, and from the third port. By being output and supplied to the antenna, only the component of the transmission frequency band is transmitted from the antenna,
A received wave input from the antenna to the third port of the second circulator is output from the second port to the second band elimination filter, and the reception is received by the second band elimination filter. Only the received frequency band component of the wave is reflected and output from the first port of the second circulator, input to the third port of the first circulator, and output from the first port. By being supplied to the wireless device, only the reception frequency band component is received by the wireless device. 6. The band-pass filter circuit according to claim 5, wherein an output side of the first band elimination filter is terminated and an output side of the second band elimination filter is terminated.

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